In an electron beam drawing apparatus, electrons reflected or scattered at the surface of a specimen are reflected again by the bottom surface of an objective lens. The re-reflected electrons expose the resist on the specimen surface excluding the place which an electron beam has entered. Such exposure leads to a decrease in the drawing accuracy. To prevent this, an antireflection plate made of a low atomic number material, such as carbon, is placed below the objective lens. In the antireflection plate, holes are made to suppress the occurrence of re-reflected electrons and direct a part of reflected electrons to an electron detector.
In recent years, electron beam drawing apparatuses have been required to have a higher beam resolution due to further miniaturization of patterns. Therefore, such an object lens as causes the peak of an axial magnetic field intensity to approach the specimen surface has been used. In this case, the trajectory of a reflected electron from the position of the specimen surface is not linear, but spiral due to the effect of a magnetic field. Therefore, reflected electrons can hardly pass through linear holes which are made in the antireflection plate so as to widen upstream or through linear holes perpendicular to the specimen surface. For this reason, with an electron beam drawing apparatus which causes the objective lens to produce the peak of an axial magnetic field intensity near the specimen surface, the detectable amount of reflected electrons becomes smaller and the S/N ratio of the detected signal decreases.